ABSTRACT
The assessment of the probative value of items of evidence in a trial at court is primarily the role of the trier of fact, whether that be the jury, magistrate or judge as appropriate. A primer for courts on forensic gait analysis, published in 2017, mentions briefly the Association of Forensic Science Providers standard for reporting opinions and gives an illustration of how a likelihood ratio may be derived. The expert should describe in their report the rationale for assigning the values for the probabilities, and therefore the likelihood ratio, and give a conclusion that relates back to the fact in issue, the propositions as described at the beginning of the report. Elements of the case circumstances that would have a bearing on the probabilities for the observations must be made known to the expert. In gait analysis, the elements would include factors such as distances, angles, lighting, recording equipment, recording parameters, the weather and the nature of the incident.
